Base station, base station module and method for direction of arrival estimation

ABSTRACT

The invention relates to a base station for a radio communications network. In order to be able to enhance the resolution for a direction of arrival estimation, the base station comprises: a first phasing network ( 31 ) for forming beams (B 1 -B 4 ) for fixed reception angles; a second phasing network ( 33 ) for co-phasing and summing the signals of at least two neighbouring beams (B 2 , B 3 ), thus forming a beam (B 2-3 ) for a reception angle in-between at least those two neighbouring beams (B 2 , B 3 ), and for scaling each resulting beam (B 2-3 ) with a predetermined factor; and means for estimating the direction of arrival in the uplink from the beams (B 1 -B 4 , B 2-3 ) provided by the first and the second phasing network ( 31, 33 ). The invention equally relates to a corresponding method and to a base station module comprising such a first and second phasing network.

CROSS REFERENCE TO RELATED APPLICATION

This is a U.S. national stage application under 35 U.S.C. 371 ofinternational stage application No. PCT/EP00/13256, filed on Dec. 23,2000, which date is the filing date of this application under 35 U.S.C.§363.

FIELD OF THE INVENTION

The invention relates to a base station for a radio communicationsnetwork, a module for such a base station and a method for enhancing theangular resolution in the estimation of the direction of arrival ofsignals in the uplink in a base station of a radio communicationsnetwork.

BACKGROUND OF THE INVENTION

It is known from the state of the art to provide base stations withsmart antenna arrays which enable the output of fully steerable downlinkbeams. When employed for a user specific digital beamforming, abeamformer of such a smart antenna array is e.g. able to weight phaseangle and/or amplitude of the transmitted signals in a way that thedirection of the beam is adapted to move along with a terminal throughthe whole sector of coverage of the antenna array.

In order to be able to move a downlink beam according to the movement ofa terminal, the base station has to determine the direction in which theterminal can be found. This can be achieved by estimating the azimuthdirection of arrival of the uplink signals received by the base stationfrom the respective terminal. For receiving uplink signals, basestations often employ a fixed beam reception system, the fixed beamsbeing evaluated for estimating the direction of arrival of the uplinksignals.

For illustration, FIG. 1 shows an example of an architecture in a basestation used for the processing of signals from a single user forestimating the direction of arrival (DoA).

The part of the base station depicted in FIG. 1 comprises an uplinkdigital beam matrix 11 connected at its inputs to a uniform linearantenna array (ULA) with eight receiver antennas (not shown). The outputof the uplink digital beam matrix 11 is connected via means for standardRAKE processing 12 to means for estimating the direction of arrival ofuplink signals 13. The means for estimating the direction of arrival 13are connected on the one hand to further components of the base stationthat are not shown. On the other hand, they are, connected to processingmeans 14 suited for spreading and weighting of signals. The processingmeans 14 receive as further inputs signals from means for downlink bitprocessing 15 and output signals to means for user-specific digitalbeamforming 16. The outputs of the means for user-specific digitalbeamforming 16 are connected to eight transmit antennas (not shown). Themeans for standard RAKE 12, for estimation of the DoA 13, for downlinkbit processing 15 and the processing means 14 are used for digitalbase-band processing.

Signals entering the base station via the receive antennas are firstprocessed in the digital beam matrix 11. The digital beam matrix 11 isan M×M matrix, where M is the number of antenna elements, i.e. M=8 inthe described example. The digital beam matrix 11 generates from thereceived signals fixed reception beams in eight different directions.With the digital beam matrix 11 and the uniform linear antenna array(ULA), orthogonal beams (butler matrix) or an arbitrary set ofnon-orthogonal beams can be generated. The generated beams are input tothe means for standard RAKE 12.

After a processing on the chip level by the means for standard RAKE 12,the beams are evaluated in the means for estimation of the direction ofarrival 13 in order to be able to determine the best direction fortransmission of downlink signals. The direction of arrival of the uplinksignals can be estimated by simply measuring the power from each beam.In particular, the power in the pilot symbols in the channel estimatecan be determined. The beam direction of the beam with the highestuplink power, averaged over fast fading, is considered as the directionof arrival, to which the downlink beam is to be directed. Alternatively,the direction of arrival can be estimated with any other known methodfor determining the direction of arrival in the beam space. The meansfor estimation of the direction of arrival 13 provide the processingmeans 14 with power control and weight information for forming thedownlink beams corresponding to the determined direction of arrival.

In addition, further elements in the means for estimation of thedirection of arrival 13 forward soft bits, including the data signalstransmitted by the terminal, to the components not depicted in thefigure.

Hard bits constituting signals that are to be transmitted from thenetwork to the terminal are processed, e.g. encoded, by the means fordownlink bit processing 15 and forwarded to the processing means 14. Theprocessing means 14 are able to spread and weight those signalsaccording to the information received from the means for estimation thedirection of arrival 13. The thus processed signals are transmitted tothe means for user-specific digital beamforming 16 which transmit thesignals via the transmit antennas in a downlink beam directed to thedetermined direction of arrival of the uplink signals.

With this method, the estimation of the uplink direction of arrival isbased on a rough resolution grid in the form of the fixed beams. Thatmeans, even though in the downlink the transmission beam can be steeredcontinuously with arbitrary resolution, the accuracy of the downlinkbeamforming is limited to the uplink beam spacing. This accuracy is notadequate for downlink beam steering, if the number of beams is equal tothe number of columns in the smart antenna array. Even if the directionof arrival resolution is improved as the number of reception beams isincreased by increasing the number of receive antennas, the angularresolution is not adequate with 4-8 beams/antennas. In the uplink, theangular resolution is approximately 30° with 4 beams and approximately15° with 8 beams.

FIGS. 2 a-d show this angular distribution of the fixed uplink beams fordifferent constellations. FIG. 2 a is a diagram with the amplitude beampattern over the azimuth angle in degrees of four orthogonal beamsresulting from a 4-antenna array. FIG. 2 b is a diagram with thecorresponding amplitude beam pattern of eight orthogonal beams of a8-antenna array. In contrast, FIG. 2 c is a diagram with the amplitudebeam pattern of four non-orthogonal beams of a 4-antenna array and FIG.2 d a diagram with the amplitude beam pattern of eight non-orthogonalbeams of a 8-antenna array.

Alternatively to basing the estimation of the direction of arrival onthe power of the fixed beams, the direction of the downlink beam can beselected by transforming the channel estimates back to the elementdomain. To this end, the beamformed signals are multiplied by aninverted digital beam matrix to obtain the element space signals. Then,any known direction of arrival techniques is used in the element space.However, for practical implementations this method leads to an excessiveamount of computations.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a base station, a basestation module and a method which allow for a simple enhancement of theangular resolution in the estimation of the direction of arrival ofuplink signals.

This object is reached on the one hand with a base station for a radiocommunications network, comprising a first phasing system (or ‘network’)for forming beams for fixed reception angles out of signals provided bya receive antenna array and for outputting the signals constituting saidbeams; a second phasing system (or ‘network’) for co-phasing and summingthe signals provided by the first phasing system for at least twoneighbouring beams, thus forming a beam for a reception angle in-betweenthe at least two neighbouring beams, and for scaling amplitude and/orpower of each resulting beam with a predetermined factor, and means forestimating the direction of arrival in the uplink from the beamsprovided by the first and second phasing systems.

On the other hand, the object is readied with a method for enhancing theangular resolution in the estimation of the direction of arrival ofsignals in the uplink in a base station of a radio communicationsnetwork, comprising:

-   -   receiving uplink signals with a receive antenna array of the        base station;    -   forming first beams for fixed angles of arrival out of the        received signals in a first phasing system (or ‘network’) and        outputting the signals constituting said beams;    -   forming at least one composite beam in-between at least two        neighbouring ones of the first beams in a second phasing system        (or ‘network’) by co-phasing and summing the signals belonging        to the neighbouring beams and by scaling amplitude and/or power        of each resulting composite beam with a predetermined factor;        and    -   estimating the direction of arrival of the received signals        based on the first beams and the composite beams.

The object is equally reached with a base station module for a basestation comprising such a second phasing system.

The invention proceeds from the idea that a finer angular spectrum canbe achieved by further processing the already beamformed uplink signals,which present a relatively rough angular spectrum. The finer resolutionis achieved by simply applying multiplications and summings on thepresent fixed beams, followed by a subsequent scaling. A main advantageof the method, the base station and the base station module according tothe invention is therefore the simplicity with which a finer angularresolution for the estimation of the direction of arrival of uplinksignals is achieved.

The estimated direction of arrival is used in particular for forming adownlink beam to be transmitted in said direction.

A receive antenna array employed for receiving uplink signals from aterminal and for providing the received signals to the first phasing ofthe base station can be comprised by the base station of the inventionor form a supplementary part of the base station. The same applies for atransmit antenna array.

The first phasing system (or ‘network’) can be suited for formingorthogonal or non-orthogonal beams as fixed reception beams. Preferably,the first phasing system is moreover suited to form four or eight ofsuch beams, depending on the number of receive antennas from which itreceives uplink signals. However, any other number of receive antennasand to be formed beams can be chosen as well.

In an advantageous embodiment of the base station and the method of theinvention, co-phasing and summing of the signals of two neighbouringbeams provided by the first phasing system is carried out for allneighbouring beams formed by the first phasing system. Accordingly, thetotal number of formed beams is twice minus one the number of theoriginal beams formed by the first phasing system.

The power and/or the amplitude of the composite beams resulting from theco-phasing and summing should be scaled according to the power and/oramplitude of the original beams, in order to make the composite beamscomparable to the first beams for determining the direction of arrival.To this end, the composite beams can be scaled in a way that equal gainsare achieved for all beams. The scaling factors can also be can also beselected so that the signal-to-noise ratio (SNR) for each beam is equalin case that the same signal is arriving to each beam. Alternatively,the scaling factors can be selected so that thesignal-to-interference-and-noise ratio (SINR) for each beam is equal incase that the same signal is arriving to each beam.

In case the composite beams are formed exactly in the middle of twoneighbouring orthogonal beams, with four original orthogonal beams thescaling factor can be set to a value which compensates the loss 0.67 dBfor all composite beams and with eight original orthogonal beams to avalue which compensates the loss of 0.86 dB in order to obtain equalgains for all beams. In the case of four orthogonal beams, in order tocompensate the loss of 0.67 dB, the power correction factor is16/13.7=1.1678, while the amplitude correction factor is √{square rootover (13.7)}=1.0807.

For achieving an even finer tuning of the angular resolution with thebase station/base station module and by the method according to theinvention, the signals of neighbouring original beams are multiplied bydifferent predetermined factors before co-phasing and summing.Preferably, one factor is greater than 1 and the other factor smallerthan 1. This way, the composite beam or beams are not necessarily placedat an angle exactly in the middle of the two neighbouring beams but canbe shifted arbitrarily to any angle between the two original beams.

In this case, the scaling factor that has to be applied on the formedcomposite beams depends in addition on the factors used for multiplyingthe amplitudes.

The proposed fine tuning can be used in particular for generatingseveral beams at different angles in between two original neighbouringbeams by multiplying them with different sets of factors. Accordingly,any desired angular resolution can be obtained for estimating thedirection of arrival in the uplink.

The estimation of the direction of arrival in the uplink is preferablybased on an evaluation of the power of the beams provided by the firstand second phasing systems (or ‘networks’).

The first and second phasing systems can be analogue phasing systems,but preferably they are digital phasing systems in which a complexvalued weight vector represents each beam in the digital domain. Suchdigital phasing systems are advantageously formed by a digital beammatrix DBM.

In a digital phasing system (or ‘network’), complex weights can bestored. The complex weights are then applied to incoming signals forforming the desired beams. The complex weights of the first digitalphasing system can be predetermined in any suitable manner so they aresuited to form the predetermined number of beams at the predeterminedangles. The complex weights of the second digital phasing system aredetermined in a way that the beams provided by the first phasing systemare co-phased and summed in the second digital phasing system whenapplying the complex weights to the corresponding signals.

In the digital domain, the co-phasing of neighbouring beams can beachieved by rotating the phase angle of at least one of the vectorsrepresenting two neighbouring beams. In the case of four orthogonaloriginal beams, the phase angle of the vector representing the first oftwo neighbouring beams can e.g. be rotated by 0 and the phase angle ofthe vector representing the second of the two neighbouring beams by+3π/4 or −3π/4, depending on which beam was selected as first and whichas second beam. In the case of signals received from an antenna arraywith eight antennas, formed into eight orthogonal beams, the phase angleof the vector representing the first of two neighbouring beams can e.g.be rotated by 0 and the phase angle of the vector representing thesecond beam by +7π/8 or −7π/8.

The rotated vectors of the two neighbouring beams are then summed, thusforming a single vector. This single vector represents a singlecomposite beam in the middle of the two original neighbouring beams.

Also the multiplication of different neighbouring beams with differentfactors for fine tuning can be realised by multiplying the amplitudes ofthe corresponding vectors with different factors before rotating andsumming.

The method and the base station according to the invention can also beused for estimating the angular spreading of signals impinging at thebase station. For example, after finding the DOA with largest averagepower the corresponding power is measured also from both adjacent beams.As described above, the increment of the direction angle from one beamto the adjacent beam can be set to be arbitrarily small. If the averagedpower of the adjacent beam is above a pre-set threshold the numberdescribing the angular spread is increased by the number correspondingto the angular increment between the two adjacent beams. The thresholdcan be also adaptive. For instance, the angular aperture of the entiresector is scanned and an average value for signal strength is obtainedwhich depends on the desired signal, the interference scenario and theparticular radio environment. The level of the desired signal is thencompared to the averaged value describing the entire sector. If thedesired signal exceeds the threshold the signal power of the next beamis then calculated. This process is repeated as long as the power levelof the desired signal is above the threshold. Thus the angular spread(AS) is directly proportional to the number of beams in which theaveraged power of the desired signal is above the threshold and to theangle interval between two adjacent beams:AS=NDwhere N equals the number of adjacent beams in which the desired signalpower is above the threshold and D is the angle increment ofneighbouring beams. For example, in case of 8 original beams and 7mid-beams the angle increment D is approximately 7.5 degrees. If thesignal power exceeds the threshold in three consecutive beams theangular spread is 22.5 degrees assuming the same angle increment D frombeam to beam. It is also noted that the angle increment D may vary frombeam to beam which is the preferred case in orthogonal beams. If thesignal power exceeds the threshold in three consecutive beams theangular spread is 22.5 degrees.

The proposed base station, base station module and method areparticularly suited for an employment with WCDMA (wideband code divisionmultiplex access) and EDGE (enhanced data rate for GSM evolution; GSM:global standard for mobile communication).

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention is explained in more detail withreference to drawings, of which

FIG. 1 shows the architecture in a conventional base station for theprocessing of uplink signals from a single terminal;

FIG. 2 a shows an amplitude beam pattern of the orthogonal beams of a4-antenna array according to the prior art;

FIG. 2 b shows an amplitude beam pattern of the orthogonal beams of a8-antenna array according to the prior art;

FIG. 2 c shows an amplitude beam pattern of the non-orthogonal beams ofa 4-antenna array according to the prior art;

FIG. 2 d shows an amplitude beam pattern of the non-orthogonal beams ofan 8-antenna array according to the prior art;

FIG. 3 shows component of a base station according to a preferredembodiment of the present invention;

FIG. 4 illustrates the forming of complex weights in the first digitalphasing network according to a preferred embodiment of the presentinvention;

FIG. 5 a shows a power beam pattern for a 4-antenna array with one beamgenerated according to a preferred embodiment of the present invention;

FIG. 5 b shows an amplitude beam pattern for a 4-antenna array withthree beams generated and scaled according to a preferred embodiment ofthe present invention;

FIG. 6 a shows an amplitude beam pattern for an 8-antenna array withseven beams generated according to a preferred embodiment of the presentinvention;

FIG. 6 b shows an amplitude beam pattern for an 8-antenna array withseven beams generated with fine tuning according to a preferredembodiment of the present invention;

FIG. 7 a shows an exemplary power distribution over 8 original beamsaccording to the prior art; and

FIG. 7 b shows an exemplary power distribution over 8 original beams and7 composite beams generated in between the original 8 beams according toa preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 a-d have already been described with reference to thebackground of the invention.

FIG. 3 depicts elements of a base station according to the inventionthat are used in a method according to the invention.

In the base station of FIG. 3, a 4-antenna array is employed as receiveantenna array. Each antenna Ant1-Ant4 is connected via a low noiseamplifier LNA to a digital beam matix DBM 31, which forms a digitalphasing system (or ‘network’) and has stored complex weights. Thedigital beam matrix corresponds to the uplink digital beam matrix 11 inFIG. 1 a, except that the digital beam matrix 31 of FIG. 3 is a 4×4instead of a 8×8 matrix. A calibration unit 32 has access to the lownoise amplifiers LNA. The digital beam matrix 31 has an output line foreach of four beams B₁ to B₄. The output lines for beams B₂ and B₃ arebranched off and fed to a second digital phasing system (or ‘network’)33. Also in the second digital phasing system 33 complex weights arestored. The second digital phasing system 33 has an output for a furtherbeam B₂₋₃.

The antenna elements Ant1-Ant4 of the receive antenna array receiveuplink signals from a terminal, the signals entering the antenna arrayfrom a certain direction depending on the present location of theterminal.

The signals received by the antennas Ant1-Ant4 are amplified in the lownoise amplifiers LNA, the low noise amplifiers LNA being calibrated bythe calibrating means 32 in a way that the transmission line fromantenna elements Ant1-Ant4 to the digital beam matrix 31 can be assumedto be identical.

In the digital beam matrix 31, four orthogonal fixed reception beamsB₁-B₄ corresponding to those shown in FIG. 2 a are formed by applyingthe suitably selected and stored complex weights to the receivedsignals. The power or the amplitude of each beam indicates the strengthof reception with a certain reception angle. The beams are output andfed to means for estimating the direction of arrival, as indicated e.g.in FIG. 1.

Two neighbouring beams B₂ and B₃ are fed in addition to the seconddigital phasing network 33. The second digital phasing network 33performs a co-phasing and subsequent summing of the two beams B₂, B₃ byapplying the further complex weights to the signals belonging to thebeams B₂, B₃. These complex weights are selected such that they cause aco-phasing and summing of the received beams received from the firstdigital phasing network 31. The result of the application of the complexweights is therefore a response in a direction in the middle between thedirections of the two original beams B₂, B₃. The amplitude and the powerof this composite beam B₂ _(—) ₃, however, is somewhat reduced comparedto the original beams B₂, B₃, when assuming the same signal strength inall three directions. When the amount of the reduction is known,however, the composite beams can be scaled so that the relative gain ofthe generated beam B₂ _(—) ₃, can be used in the means for estimatingthe direction of arrival for taking into account an additional azimuthangle.

It is now explained with reference to FIG. 4 how the scaling factor canbe obtained for orthogonal beams of the 4-antenna array used in the basestation of FIG. 3.

Co-phasing of two adjacent beams can be achieved by co-phasing thecomplex valued weight vectors representing two neighbouring beams in thedigital beam matrix 31 in the digital domain. The vector b_(i) for beamB_(i) is obtained by summing the elements a_(k) of the correspondingarray response vector a_(i):$b_{i} = {\sum\limits_{k = 1}^{N}\quad a_{k}}$

FIG. 4 illustrates in vector form how a digital beam matrix 31 used forgenerating four orthogonal beams B₁-B₄ determines complex valued weightvectors for beams B₂ and B₃. Given a 4-beam digital beam matrix, theelements of the corresponding vector are added for beam B₂, while thephase angle is rotated from one element to the next by 45°, as shown onthe left hand side of FIG. 4. The resulting vector is b₂=1+2,414j.Similarly, the signals from the antenna elements are added for beam B₃,but here the phase angle is rotated from one element to the next by−45°, as shown on the right hand side of FIG. 4. The resulting vector inthis case is b₃=1−2,414j. Beam B₂ and beam B₃ are represented in thedigital domain by these vectors b₂ and b₃.

The output of the first digital phasing network 31 can be co-phased byrotating the phase angle of beam B₂ or beam B₃ or both. Here, the phaseangle of beam B₃ is rotated by 3π/4 to co-phase with beam B₂. Afterco-phasing, the beams are summed, leading to a composite beam B₂ _(—) ₃represented by

 b ₂ _(—) ₃ =b ₂ +b ₃=2+4.83j=5.23 exp(j3π/8).

While the power of the four beams B₁ to B₄ output by the digital beammatrix 31 is 16, the power of the resulting beam B₂ _(—) ₃ is0.5*(5.23)²=13.7. Thus, the loss compared to the original beam is13.7/16=0.67 dB. The knowledge of this loss enables a scaling of a beamgenerated in the middle of two fixed beams so that the relative gain ofthe generated beam is known and can be used for estimating the directionof arrival. The scaling factors are stored as well as the requiredcomplex weights.

For other kinds of digital beam matrices the scaling factors aredetermined analogously. With an 8-antenna array and a digital beammatrix forming 8 non-orthogonal beams B₁-B₈, for example, the outputsfor the two centre beams, B₄ and B₅, are b₄=1+5.03j and b₅=1−5.03j.After co-phasing the two beams B₄, B₅ by rotating B₅ by 7π/8, thecomposite beam B₄ _(—) ₅ is represented byb ₄ _(—) ₅ =b ₄ +b ₅=2+10.05j=10.25 exp(j7π/16),the power being 52.5 as compared to 64 for the original beams B₁-B₈.Therefore, the loss in the antenna gain in this case is 52.5/64=0.86 dBfor an 8-beam digital beam matrix.

Instead of two adjacent beams, also more beams can be co-phased andsummed to obtain mid-beams.

FIG. 5 a is a diagram of the power beam pattern obtained by the basestation of FIG. 3 without scaling in case of orthogonal Butler beams.The power is depicted over the azimuth angle from −100 to 100. As can beseen in the diagram, the power of the four original beams B₁ to B₄ is16, while the power of the composite beam B₂ _(—) ₃ is 13.7, in linewith the above calculation of the scaling factors.

FIG. 5 b shows a diagram with the amplitude beam pattern of fouroriginal beams and three composite beams in case of non-orthogonalbeams, where the beams are roughly scaled with corresponding scalingfactors. The composite beams B₁ _(—) ₂, B₂ _(—) ₃, B₃ _(—) ₄ have beenformed between each existing pair of neighbouring original beams B₁/B₂,B₂/B₃ and B₃/B₄. It becomes apparent from this figure that the directionof arrival resolution can be doubled by introducing a composite beam inbetween all neighbouring original beams.

In another embodiment of the method according to the invention, afurther increase of the angular resolution can be obtained.

The above described embodiment applies only phase shifts to the originalbeams, which provides one additional beam exactly between twoneighbouring beams. Providing such generated composite beams is notsufficient, if there is a need for fine tuning the directions of thecomposite beams.

In order to be able to achieve a finer resolution, complex weightscausing phase shifts and amplitude adjustments to the received beams areapplied for neighbouring beams. This way, a composite beam can bedirected into any desired direction.

FIGS. 6 a and 6 b illustrate the difference between beamforming by phaseshifting only and beamforming by phase shifting and an additionaladjustment of the amplitudes of the original beams.

FIG. 6 a is a diagram of the amplitude beam pattern from a 8-beamdigital beam matrix forming 8 orthogonal beams B_(i) (i=1 to 8). Theadditional composite beam pattern for seven composite beams B_(i) _(—)_(i+1) results from co-phasing and summing all neighbouring originalbeams B_(i) and B_(i+1) (i=1 to 7). Co-phasing was achieved by phaseshifting the phase φ_(i) of the first one of two neighbouring beamsB_(i) by Δφ_(i)=0 and the phase φ_(i+1) of the second one of twoneighbouring beams B_(i+1) by Δφ_(i+1)=−7π/8 for all pairs ofneighbouring beams. The composite beams have not been scaled, thereforethey appear in the figure with a lower amplitude than the originalbeams.

In FIG. 6 b, in addition to the phase shifts of Δφ_(i)=0 andΔφ_(i+1)=−7π/8, the amplitude of the respective first neighbouring beamB_(i) was multiplied by 0.8 and the amplitude of the respective secondneighbouring beam B_(i+1) by 1.2 before summing. As a result, thegenerated composite beams B_(i) _(—) _(i+1) in FIG. 6 b are shiftedsomewhat to the left as compared to the composite beams in FIG. 6 a. Byvarying the factors with which the amplitudes of the original beams aremultiplied, the composite beams can thus be positioned at any anglebetween two original beams.

This approach enables in addition that several beams can be formedbetween every two neighbouring original beams simply by applyingdifferent sets of factors for the multiplication of the amplitudes ofthe original beams, which leads to an arbitrarily fine angularresolution.

Finally, FIGS. 7 a and 7 b show the power distribution over differentnon-orthogonal beams used in a base station by means for estimation ofthe direction of arrival of uplink signals. Both distributionscorrespond to the case that the signals from the terminal reach thereceive antenna array of the base station perpendicularly, which is hereto correspond to an azimuth angle of 0°. In FIG. 7 a, the direction ofarrival is to be estimated from the power distribution over 8 beams, allbeing formed by a first digital phasing network. The relation betweenthe different beams and the different angles of arrival are the same ase.g. in FIG. 2 d. In FIG. 7 b, in contrast, the direction of arrival isto be estimated from the power distribution over 15 beams, including 7composite beams formed in between the 8 original beams according to theinvention. As can be seen in FIG. 7 a, beams number 4 and number 5 havethe maximum power. Accordingly, the means for estimating the directionof arrival are not able to determine the best direction for the downlinkbeam but only a best area which is lying between the angles of beamnumber 4 and beam number 5. In FIG. 7 b, the maximum power belongsclearly to beam number 8, positioned exactly between original beams 4(here beam 7) and original beam 5 (here beam 9) and therefore at anangle of 0°. This shows that in the latter case, the best direction forthe downlink beam can be determined much more accurately.

1. A base station for a radio communications network, comprising: afirst phasing system for forming beams for fixed reception angles out ofsignals provided by a receive antenna array and for outputting thesignals constituting said beams; a second phasing system for co-phasingand summing the signals provided by the first phasing system for atleast two neighbouring beams, thus forming a beam for a reception anglein-between the at least two neighbouring beams, and for scaling at leastone of amplitude and power of each resulting beam with a predeterminedfactor; means for estimating the direction of arrival in the uplink fromthe beams provided by the first and the second phasing systems; andmeans for estimating the angular spreading of the received signals basedon the beams formed by the first and the second phasing system.
 2. Thebase station of claim 1, further comprising: the receive antenna arrayfor receiving signals from a terminal and for providing the receivedsignals to the first phasing system of the base station; and a transmitantenna array for transmitting a beam in the estimated direction ofarrival.
 3. The base station of claim 1, wherein the first phasingsystem is designed to form orthogonal fixed reception beams.
 4. The basestation of claim 1, wherein the first phasing system is designed to formnon-orthogonal fixed reception beams.
 5. The base station of claim 1,wherein the first phasing system is designed to form four beams out ofthe signals received from four receive antennas.
 6. The base station ofclaim 1, wherein the first phasing system is designed to form eightbeams out of the signals received from eight receive antennas.
 7. Thebase station of claim 1, wherein the second phasing system is suited forscaling at least one of amplitude and power of the beams formed inbetween two neighbouring beams according to the at least one ofamplitude and power of the beams formed by the first phasing system in away that the gain of all formed beams is equal.
 8. The base station ofclaim 1, wherein the second phasing system is suited for scaling atleast one of amplitude and power of the beams formed in between twoneighbouring beams according to the at least one of amplitude and powerof the beams formed by the first phasing system in a way that thesignal-to-noise ratio for each formed beam is equal when each beam fromthe first phasing system is equal in power and/or amplitude.
 9. The basestation of claim 1, wherein the second phasing system is suited forscaling at least one of amplitude and power of the beams formed inbetween two neighbouring beams according to the at least one ofamplitude and power of the beams formed by the first phasing system in away that the signal-to-interference-and-noise ratio for each formed beamis equal when each beam from the first phasing system is equal in powerand/or amplitude.
 10. The base station of claim 1, wherein the secondphasing system is suited for co-phasing and summing the signals of allneighbouring beams formed by the first phasing system.
 11. The basestation of claim 1, wherein the second phasing system is suited formultiplying the signals provided by the first phasing system for twoneighbouring beams (B_(i), B_(i+1)) in between which a composite beam(B_(i) _(—) ₊₁) is to be formed with at least one pair of differentpredetermined factors before co-phasing and summing in order to obtainat least one beam in-between the two neighbouring beams at at least onepredetermined azimuth angle.
 12. The base station of claim 1, whereinthe means for estimating the direction of arrival in the uplink aresuited to evaluate the power of the beams provided by the first and thesecond phasing system for estimating the direction of arrival.
 13. Thebase station of claim 1, wherein the first and the second phasingsystems are analogue phasing systems.
 14. The base station of claim 1,wherein the first and the second phasing systems are digital phasingsystems in which a complex valued weight vector represents each beam inthe digital domain.
 15. The base station of to claim 14, wherein, in thefirst and the second digital phasing systems, complex weights are storedthat are to be applied to incoming signals for forming the respectivebeams.
 16. The base station of claim 1, wherein the second phasingsystem is suited for co-phasing and summing at least two neighbouringbeams by rotating the phase angle of at least one of the vectorsrepresenting one of the two neighbouring beams for obtaining two vectorswith the same phase angle and by summing said vectors for obtaining asingle vector representing a beam in between the two neighbouring beams.17. A method for enhancing the angular resolution in the estimation ofthe direction of arrival of signals in the uplink in a base station of aradio communications network, comprising the steps of: receiving uplinksignals with a receive antenna array of the base station; forming firstbeams for fixed angles of arrival out of the received signals in a firstphasing system and outputting the signals constituting said beams;forming at least one composite beam in-between at least two neighbouringones of the first beams in a second phasing system by co-phasing andsumming the signals belonging to the neighbouring beams and by scalingat least one of amplitude and power of each resulting composite beamwith a predetermined factor; estimating the direction of arrival of thereceived signals based on the first beams and the at least one compositebeam; and estimating the angular spreading of the received signals basedon the formed first and at least one composite beam.
 18. The method ofclaim 17, further comprising: forming and outputting a downlink beam inthe estimated direction of arrival of the uplink signals.
 19. The methodof claim 17, wherein at least one of amplitude and power of the beamsformed in between two neighbouring beams are scaled according to the atleast one of amplitude and power of the beams formed by the firstphasing system.
 20. The method of claim 17, wherein the factor forscaling is set to a value leading to an equal gain for each formed beam.21. A method for enhancing the angular resolution in the estimation ofthe direction of arrival of signals in the uplink in a base station of aradio communications network, comprising the steps of: receiving uplinksignals with a receive antenna array of the base station: forming firstbeams for fixed angles of arrival out of the received signals in a firstphasing system and outputting the signals constituting said beams;forming at least one composite beam in-between at least two neighbouringones of the belonging to the neighbouring beams and by scaling at leastone of amplitude and power of each resulting composite beam with apredetermined factor, wherein the factor for scaling is set to a valueleading to an equal gain which compensates the loss of 0.67 dB for allbeams formed exactly in the middle of two neighbouring first beams incase of a receive antenna array with four antennas and orthogonal firstbeams; estimating the direction of arrival of the received signals basedon the first beams and the at least one composite beam.
 22. A method forenhancing the angular resolution in the estimation of the direction ofarrival of signals in the uplink in a base station of a radiocommunications network, comprising the steps of: receiving uplinksignals with a receive antenna array of the base station; forming firstbeams for fixed angles of arrival out of the received signals in a firstphasing system and outputting the signals constituting said beams;forming at least one composite beam in-between at least two neighbouringones of the first beams in a second phasing system by co-phasing andsumming the signals belonging to the neighbouring beams and by scalingat least one of amplitude and power of each resulting composite beamwith a predetermined factor, wherein the factor for scaling is set to avalue leading to an equal gain which compensates the loss of 0.86 dB forall beams formed exactly in the middle of two neighbouring beams in caseof a receive antenna array with eight antennas and orthogonal firstbeams; estimating the direction of arrival of the received signals basedon the first beams and the at least one composite beam.
 23. The methodof claim 17, wherein the factor for scaling is set to a value leading toan equal signal-to-noise ratio (SNR) for each formed beam.
 24. Themethod of claim 17, wherein the factor for scaling is set to a valueleading to an equal signal-to-interference-and-noise ratio (SINR) foreach formed beam.
 25. The method of claim 17, wherein the second phasingsystem forms composite beams in between each of the neighbouring firstbeams formed by the first phasing system.
 26. The method of claim 17,further comprising the step of: multiplying the signals provided by thefirst phasing system for two neighbouring beams (B_(i), B_(i+1)) inbetween which a composite beam (B_(i) _(—) _(i+1)) is to be formed witha different predetermined factor before co-phasing and summing in orderto obtain a beam in-between the two neighbouring beams at apredetermined azimuth angle.
 27. The method of claim 17, furthercomprising the step of: multiplying the signals provided by the firstphasing system for two neighbouring beams with different pairs ofpredetermined factors in order to obtain differently weighted pairs ofsignals for each of the neighbouring beams, and subsequently co-phasingand summing each pair of signals in order to obtain a plurality of beamsin between the two neighbouring beams at predetermined azimuth angles.28. The method of claim 17, wherein the beams are formed by analoguefirst and second phasing systems.
 29. The method of claim 17, whereinthe beams are formed by digital first and second phasing systems inwhich a complex valued weight vector represents each beam in the digitaldomain.
 30. A method for enhancing the angular resolution in theestimation of the direction of arrival of signals in the uplink in abase station of a radio communications network, comprising the steps of:receiving uplink signals with a receive antenna array of the basestation; forming first beams for fixed angles of arrival by applyingcomplex weights to the received signals in a first digital phasingsystem to thereby output a plurality of complex valued weight vectors,each representing a first beam in the digital domain; forming at leastone composite beam in-between at least two neighbouring ones of thefirst beams in a second digital phasing system by performing thesub-steps of: co-phasing and summing the signals of neighbouring firstbeams by applying to said signals of the formed first beams complexweights causing a phase angle rotation of at least one of the vectorsrepresenting the two neighbouring beams to thereby obtain two vectorswith the same phase angle and by summing said vectors; and scaling atleast one of amplitude and power of each resulting composite beam with apredetermined factor; and estimating the direction of arrival of thereceived signals based on the first beams and the at least one compositebeam.
 31. The method of claim 30, wherein the co-phasing is carried outby rotating the phase angles of the vectors of two neighbouring beams by0 and |3π/4|, respectively, in case of a receive antenna array with fourantennas and orthogonal first beams.
 32. The method of claim 30, whereinthe co-phasing is carried out by rotating the phase angles of thevectors of two neighbouring beams by 0 and |7π/8|, respectively, in caseof a receive antenna array with eight antennas and orthogonal firstbeams.
 33. A system for improving angular resolution of a receiveantenna array of a base station in a radio communications network,wherein said base station comprises a first phasing system for formingbeams for fixed reception angles out of signals received from thereceive antenna array and for outputting the signals constituting saidbeams, comprising: a second phasing system for co-phasing and summingthe signals provided by the first phasing system for at least twoneighboring beams, thus forming at least one composite beam for areception angle in-between the at least two neighbouring beams, and forscaling at least one of amplitude and power of each resulting at leastone composite beam with a predetermined factor, said second phasingsystem comprising: a means for multiplying the signals provided by thefirst phasing system for the at least two neighbouring beams (B_(i),B_(i+1)) with at least one pair of different predetermined factorsbefore co-phasing and summing the provided signals in order to form theat least one composite beam (B_(i) _(—) _(i+1)) at a predeterminedazimuth angle; wherein the means for estimating the direction of arrivalin the uplink is provided with the beams from the first phasing systemand the at least one composite beam from the second phasing system. 34.A base station for a radio communications network, comprising: a firstphasing system for forming beams for fixed reception angles out ofsignals provided by a receive antenna array and for outputting thesignals constituting said beams; a second phasing system for co-phasingthe signals provided by the first phasing system for at least twoneighbouring beams by rotating the phase angle of at least one of thevectors representing one of the two neighbouring beams in order toobtain two vectors with the same phase angle, for summing said obtainedvectors in order to obtain a single vector representing a beam for areception angle in between the two neighbouring beams, and for scalingat least one of amplitude and power of each resulting beam with apredetermined factor; and means for estimating the direction of arrivalin the uplink from the beams provided by the first and the secondphasing systems.
 35. A base station for a radio communications network,comprising: a first phasing system for forming beams for fixed receptionangles out of signals provided by a receive antenna array and foroutputting the signals constituting said beams; a second phasing systemfor multiplying the signals provided by the first phasing system for twoneighbouring beams (B_(i), B_(i+1)) in between which a composite beam(B_(i) _(—) _(i+1)) is to be formed with at least one pair of differentpredetermined factors, for co-phasing and summing the multiplied signalsin order to obtain at least one beam in-between the two neighbouringbeams at at least one predetermined azimuth angle, and for scaling atleast one of amplitude and power of each resulting beam with apredetermined factor; and means for estimating the direction of arrivalin the uplink from the beams provided by the first and the secondphasing systems.
 36. A method for enhancing the angular resolution inthe estimation of the direction of arrival of signals in the uplink in abase station of a radio communications network, comprising the steps of:receiving uplink signals with a receive antenna array of the basestation; forming first beams for fixed angles of arrival out of thereceived signals in a first phasing system and outputting the signalsconstituting said beams; forming at least one composite beams byperforming, for each composite beam, the sub-steps of: multiplying thesignals output by the first phasing system for two neighbouring firstbeams (B_(i), B_(i+1)) in between which a composite beam (B_(i) _(—)_(i+1)) is to be formed with a first predetermined factor; co-phasingand summing the multiplied signals of the two neighbouring first beams(B_(i), B_(i+1)) in a second phasing system to obtain a composite beam(B_(i) _(—) _(i+1)) at a predetermined azimuth angle in-between the twoneighbouring first beams (B_(i), B_(i+1)); and scaling at least one ofamplitude and power of the resulting composite beam (B_(i) _(—) _(i+1))with a second predetermined factor; and estimating the direction ofarrival of the received signals based on the first beams and the atleast one composite beam.
 37. A method for enhancing the angularresolution in the estimation of the direction of arrival of signals inthe uplink in a base station of a radio communications network,comprising the steps of: receiving uplink signals with a receive antennaarray of the base station; forming first beams for fixed angles ofarrival out of the received signals by a first phasing system andoutputting the signals constituting said beams; forming a plurality ofcomposite beams by performing, for each composite beam, the sub-stepsof: multiplying the signals output by the first phasing system for twoneighbouring first beams with different pairs of first predeterminedfactors in order to obtain differently weighted pairs of signals foreach of the two neighbouring first beams; co-phasing and summing eachpair of signals by a second phasing system in order to obtain aplurality of composite beams at predetermined azimuth angles in-betweenthe at least two neighbouring first beams; and scaling at least one ofamplitude and power of each resulting composite beam with a secondpredetermined factor; and estimating the direction of arrival of thereceived signals based on the first beams and the plural compositebeams.